The present invention relates to molded, cellular, polyurethane articles having internal mold release capabilities, compositions for use in the preparation of such articles, and methods of making such articles. More particularly, the invention relates to rigid, cellular molded polyurethane articles produced by structural reaction injection molding (SRIM) processes. The molded articles of the invention may be characterized as having densities ranging from 15 to 40 pcf. Most particularly, the invention relates to rigid, cellular polyurethane SRIM articles having fiberglass reinforcement therein, the articles having internal mold release capabilities.
Molded cellular and noncellular polyurethane articles have found many applications in the automotive and building industries. Illustrative automotive applications include the use of such articles as consoles, door panels, pillars and seat backs. Examples of non-automotive uses include modular housing and shower supports and doors. Although many polyurethane molded parts are produced by reaction injection molding processes (RIM), it has been found that the use of woven or non-woven fiber reinforcements can provide parts with greater tensile strength and flex modules. Such molding processes are known as structural reaction injection molding (SRIM).
SRIM processes may be generally described as the pouring or injecting of a liquid foam composition into a closed or open mold which, if open, is subsequently closed during the foaming reaction. Prior to the pouring in of the liquid foam composition, reinforcing fiberglass mats and/or other suitable plastic reinforcing parts are placed in the open mold. In some cases, a cosmetic facing or cover stock material will initially be laid in the open mold prior to the placement of the reinforcing materials and/or liquid foaming composition. When such cover stock materials are used, and the liquid foam composition is subsequently poured into the partially filled mold, the process is known as a back filling or pour-behind SRIM process.
Although SRIM molders are faced with problems unique to their particular processes, they are also faced with the problems attendant to any traditional polyurethane molding process. In any molding operation, efficiency and cost considerations mandate that the length of time required to make each part be minimized as much as possible. As a result, it is highly desirable that each part be removed from the mold as rapidly and as easily as possible.
However, those skilled in the art will appreciate that molded polyurethane parts often resist release from the mold. Traditionally, external mold release (EMR) agents have been sprayed onto the mold surface each time a new part is to be molded. The use of such EMR agents is highly disadvantageous for two reasons. First, the use of the EMR agents adds significantly to the per part cost. Factors such as the cost of the EMR agent per application, the cost of the labor or equipment required to apply the EMR agent, and the cost of the time during which the mold is open but is nonfunctioning, must all be included when evaluating the additional cost per part resulting from the use of EMR agents. Second, the EMR agents often include volatile components which results in a need for air cleaning and/or ventilation equipment. Fans, blowers, and protective gear all represent a significant capital investment.
As a result, polyurethane molders have long desired internal mold release (IMR) agents which are mixed with one or more of the polyurethane components and are thus present during each molding cycle. Such internal mold release agents are intended to appear at the interface between the mold wall cavity and the reacting ingredients to effect sufficient non-adherence between the two so that release and removal of the molded article can be easily accomplished.
Examples of previous prior art attempts to provide IMR agents are disclosed in several U.S. patents. Illustrative is U.S. Pat. No. 5,283,311, which discloses fatty prepolymers and fatty modified organic polyisocyanates as internal mold release agents useful in RIM processes.
GB 2,101,140A discloses an internal mold release agent comprising the reaction product of heating a metal salt such a zinc stearate with an epoxidized vegetable oil such as epoxidized soybean oil.
U.S. Pat. No. 5,244,931, commonly assigned to BASF Corporation, discloses that when epoxidized 2-ethylhexyltalate is used in conjunction with a cell opening mixture of a particular dibasic acid ester claimed therein, the resulting articles have improved mold release characteristics. U.S. Pat. Nos. 4,052,495 and 4,457,887, assigned to Dow Corning Corporation, respectively disclose siloxane-polyoxyalkylene copolymers and silicones intended for use as internal mold release agents in the molding of polyurethanes articles.
Similarly, U.S. Pat. Nos. 4,498,929, 4,546,145, 4,504,314, and 4,477,366, assigned to ICI, disclose internal mold release agents incorporating particular polysiloxane compounds.
However, very few prior art attempts at providing internal mold release agents have been successfully directed towards SRIM applications. The process of molding SRIM articles provides unique challenges to the successful incorporation of IMR agents. The use of the IMR agents must not interfere with or detract from the internal adhesion of the polyurethane composition to internal components like the fiberglass mat and/or polymer based structural reinforcing elements. Likewise, the IMR agent on the exterior surface of the finished SRIM article must not interfere with adhesion between the article and external components like cover stocks used in a pour-behind SRIM applications. Finally, the use of the IMR agents must not interfere with the flow characteristics or reactivity profile of the polyurethane composition. Those skilled in the art will appreciate that the polyurethane compositions used in SRIM applications must exhibit superior flowability and generally low viscosity in order to accommodate the presence of the reinforcing materials.
In addition to the performance requirements of the finished SRIM article, those skilled in the art will appreciate that it would be highly desirable to achieve polyol compositions capable of providing internal mold release properties which do not exhibit separation behavior upon standing. Those skilled in the art will appreciate that IMR agents often exhibit separation behavior when combined in either the polyol component or the isocyanate component of a polyurethane composition. Such separation behavior represents special processing challenges and often requires the use of costly processing and/or mixing equipment.
It is thus an object of the invention to provide an internal mold release agent which is capable of use in SRIM compositions and applications and which reduces the need to apply EMR agents.
It is a further object of the invention to provide a polyol composition having an internal mold release agent therein which does not exhibit separation behavior and which, when used in SRIM applications, provides rigid, cellular polyurethane articles exhibiting good adhesion to both internal and external components.
It is a further object of the instant invention to provide a foam composition for the preparation of molded polyurethane articles having internal mold release properties, wherein the polyol component of the composition exhibits little or no separation behavior and the composition results in rigid, cellular polyurethane articles exhibiting good adhesion to both internal and external component elements.
Finally, it is an object of the invention to provide improved methods of making SRIM articles, wherein the articles have internal mold release properties and the need to apply EMR agents is reduced.